What boat is it Dave?
As far as the marina's canvas shop pricing, I think I'd start by figuring out how much money you have, and then give all of it to them. LOL
I think a "cockpit cover" and "morring cover" are one in the same. A full cover, bow to stern (like a car cover) I'd call a.......wait for it.....full cover.
I'd think the best for dry storage would be a full cover, as that would keep dust, bird droppings, and droppings from boats racked above yours, off of your boat. I'm guessing, though, that the valet service will not place the cover on the boat when they rack/un-rack it. Might check with them though, see if you can work out a deal.